bug#73900: 30.0.91; auto-fill adds extra space in js-ts-mode

[Yuan Fu <casouri@gmail.com>]

> On Oct 27, 2024, at 8:10 PM, Dmitry Gutov <dmitry@gutov.dev> wrote:
> 
> On 27/10/2024 12:55, Eli Zaretskii wrote:
>>> From: Michael Kleehammer<michael@kleehammer.com>
>>> Date: Sat, 19 Oct 2024 22:46:55 -0500
>>> 
>>> In Emacs 30, js-ts-mode auto-fill chooses an incorrect prefix when
>>> wrapping comments.
>>> 
>>> 1) emacs -Q
>>> 
>>> 2) In the scratch buffer:
>>>    a) M-x js-ts-mode
>>>    b) M-x auto-fill-mode
>>>    c) M-x erase-buffer
>>>    3) Paste in a long JS comment:
>>> 
>>>    // This buffer is for text that is not saved, and for Lisp evaluation.  To create a file, visit it
>>> 
>>> 4) At end of line, press <Space>.
>>> 
>>> The text wraps like so:
>>> 
>>>    // This buffer is for text that is not saved, and for Lisp evaluation.
>>>    //   To create a file, visit it
>>> 
>>> In previous versions, it would wrap like so:
>>> 
>>>    // This buffer is for text that is not saved, and for Lisp evaluation.
>>>    // To create a file, visit it
>> Adding people who know about js-ts-mode, in the hope they will have
>> comments or suggestions.
> 
> I suppose the answer is somewhere around the fact that we have both normal-auto-fill-function and fill-paragraph-function, and that js-ts-mode (through c-ts-common-comment-setup) only configures the latter, while js-mode (in js--mode-setup) has settings for both.
> 
> Not sure why the default do-auto-fill doesn't skip over the space, though.

Ok, so the actually difference is in comment-line-break-function, which auto-fill-mode uses to insert line break. In js-mode, it’s set to c-indent-new-comment-line, which deletes the whitespace; in tree-sitter mode, it’s c-ts-common-comment-indent-new-line, which doesn’t. I fixed c-ts-common-comment-indent-new-line to do the same thing as c-indent-new-comment-line.

However, I did the foolish thing of pushing to master. Should I cherry pick the commit into emacs-30? Would that create any merge conflict down the line?

Yuan